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This paper focusses on invasions of riparian zones by exotic plants, considering mainly the proportion of exotic taxa within the plant communities. The functioning and the landscape structures of riparian corridors may suggest a high degree of invasibility of these ecosystems encouraging the spread of exotic organisms at the regional scale through the hydrological network. Examples taken in SW France, NW USA and SE Spain showed that invasion patterns are very scale-sensitive. Under oceanic climates, longitudinal regular trends are consistent between France and USA. They are mainly explained by the disturbance regime gradient. by geomorphological attributes, by human influence and by climatic influences. However, no correlation was observed between the percentage of exotics and the species richness of the community. Such a positive correlation was observed at an intermediate scale (river stretch) among the patches of the riparian mosaic. Semi-arid streams did not show any regular trend or any correlation between % of exotics and species richness. Comparisons with the litterature show that, despite a high potential of invisibility. riparian zones occupy a medium position together with other linear and/or disturbed systems when considering actual invasions in terms of % of species. The observed patterns are discussed with reference to the management of landscape structures for practical issues in conservation biology.